The present invention relates to anisotropic conductive adhesives used for electric connection between a semiconductor element and a flexible wiring board, for example.
Adhesives containing conductive particles have been used as means for connecting a semiconductor element and a flexible wiring board, for example.
Reference 130 in FIG. 8(a) represents a semiconductor element comprising an element body 131, a wiring film 135 provided on the top of element body 131 and a protective film 137 provided on wiring film 135 and having an opening 139 at a predetermined location.
Reference 110 in FIG. 8(a) represents a flexible wiring board to be connected to semiconductor element 130, and the flexible wiring board 110 comprises a base film 111 and a wiring film 115 formed on base film 111.
Wiring films 115, 135 of flexible wiring board 110 and semiconductor element 130 have connector parts 115a, 135a serving for the connection described later and wiring parts 115b, 135b running around in flexible wiring board 110 and semiconductor element 130 and connected at one end to connector parts 115a, 135a, respectively.
Opening 139 in protective film 137 is located on connector part 135a of semiconductor element 130. In the opening 139 is provided a bump 136 upright on connector part 135a with the top of bump 136 projecting from the surface of protective film 137.
The flexible wiring board 110 and semiconductor element 130 are connected by first opposing the side of semiconductor element 130 having protective film 137 and the side of flexible wiring board 110 having wiring film 115 to each other and inserting an adhesive film 120 made of an adhesive containing conductive particles 125 between both, as shown in FIG. 8(a).
Then, adhesive film 120 is sandwiched between semiconductor element 130 and flexible wiring board 110 while aligning bump 136 on semiconductor element 130 to face connector part 115a of wiring film 115 of flexible wiring board 110, and the assembly is heated under pressure so that adhesive film 120 softens by heating so that the softened adhesive film 120 is displaced from the top of bump 136 of semiconductor 130 and the remaining adhesive film 120 is sandwiched between connector part 115a and bump 136.
FIG. 8(b) shows this state, in which conductive particles 125 in adhesive film 120 sandwiched between bump 136 and connector part 115a enter into the surface of the top of bump 136 and the surface of connector part 115a under pressure to connect wiring films 115, 135 via the conductive particles 125.
Reference 100 in FIG. 8(b) represents an electric device obtained by heating, pressing and then cooling.
As adhesive film 120 hardens when it is cooled after heating, semiconductor element 130 and flexible wiring board 110 are not only electrically but also mechanically connected via conductive particles 125 in the electric device 100.
A part of flexible wiring board 110 distant from connector part 115 to be connected to bump 136 is pressed against the surface of protective film 137 of semiconductor element 130 during heating under pressure because of its flexibility so that protective film 137 of semiconductor element 130 and wiring film 115 of flexible wiring board 110 come into close contact with each other.
As conductive particles 125 used in adhesive film 120 normally have an average particle diameter greater than the thickness of protective film 137 of semiconductor element 130 and made of a rigid metal, conductive particles 125 may break through protective film 137 under pressure when the surface of protective film 137 of semiconductor element 130 and the surface of flexible wiring board 110 come into close contact with each other.
The right half of FIG. 8(b) is a schematic sectional view showing that conductive particles 125 have broken through protective film 137, and the conductive particles 125 having broken through protective film 137 may come into contact with wiring parts 115b, 135b to cause short circuit in wiring films 115, 135 forming electric device 100 when wiring parts 115b, 135b of wiring films 115, 135 are faced to each other in the zone where flexible wiring board 110 and semiconductor element 130 are in close contact with each other.
With high densification of electronic components, the pattern of wiring film 135 of semiconductor 130 is becoming finer in recent years, so that when conductive particles 125 having broken through protective film 137 enter between wiring film members 135, adjacent wiring film members 135 may be electrically connected via conductive particles 125 to cause short circuit between wiring film members 135 of semiconductor element 130.
It is also possible to directly apply an adhesive on the surface of flexible wiring board 110 for connection to semiconductor element 130 without forming it into a film, but such an adhesive may readily cause connection failure because the conductive particles 125 are not homogeneously dispersed in the pasty adhesive and tend to precipitate.
The present invention was made to solve the problems of the prior art described above with the purpose of providing an adhesive film having high reliability of connection to fine-pitch circuits.
In order to solve the above problems, the present invention provides an adhesive comprising an insulating adhesive component and conductive particles dispersed in the insulating adhesive component wherein the conductive particles have an average diameter of from 10 nm or more to 90 nm or less.
The present invention provides the adhesive characterized in that the conductive particles contained in the adhesive have a specific surface area of from 5 m2/g or more to 80 m2/g or less.
The present invention provides the adhesive characterized in that the conductive particles contained in the adhesive represent a total volume of from more than 0.1% to less than 12% on the basis of the total volume of the insulating adhesive component and the conductive particles.
The present invention provides the adhesive characterized in that the conductive particles are based on at least one metal selected from the group consisting of nickel, palladium, copper, iron and silver.
The present invention provides the adhesive characterized in that the insulating adhesive component preferably contains an epoxy resin and an imidazole-based latent curing agent.
The present invention provides the adhesive characterized in that the adhesive has a viscosity of 1000 Pa.s or less at 25xc2x0 C.
The present invention provides an adhesive film made of an adhesive in the form of a film comprising an insulating adhesive component and conductive particles dispersed in the insulating adhesive component wherein the conductive particles have an average diameter of from 10 nm or more to 90 nm or less.
The present invention provides an electric device comprising a semiconductor element and a wiring board, wherein the semiconductor element is adhesively bonded to the wiring board with the adhesive comprising an insulating adhesive component and conductive particles dispersed in the insulating adhesive component wherein the conductive particles have an average diameter of from 10 nm or more to 90 nm or less.